The invention concerns the improvement of the effect of the process technique and the practicability of so-called extruders, expanders or similar apparatus, especially for the thermal treatment of substances and substance mixtures, particularly in the food industry, feed industry and fertilizer industry. However, the invention is also advantageous inn the same manner in the pharmaceutical field, as well as for the production and processing of plastic articles.
Individual products and compounds, but also substance mixtures, are subjected to a reaction or a treatment under specified process parameters, such as contact time, temperature, pressure, quantity ratios, etc., and are subsequently expelled from a continuously operating system, optionally under simultaneous relaxation and/or shaping. For the continuous advance of material through a reaction or treatment zone, there are used, preferably if not exclusively, screw elements, including double or multiple screws, which are horizontally disposed in a closed system, such as an extruder. The screw channels defined by the screw elements can change within the system to allow adjustment for transporting different materials and for different contact times as well as altogether variable and differentiated reaction conditions.
It is known to insert so-called scraper fingers or breaker rods, which are oriented radially from an inner surface of a screw casing, or jacket, which extends in the direction of the screw shaft, in order to provide for the mechanical lifting of material during the continuous transport of material through the screw volume. Such scraper fingers serve for the constant lifting or break-up of soft or semiplastic material, as well as agglomerated material, during the continuous passage of the material through the treatment zone so as to assure an optimum renewal of the surface and, thus, to assure that the treatment process can be carried out as intended. The mechanical lifting of the material with the simultaneous renewal of the surface is necessary particularly when the material or products tend to cake or adhere, in order to prevent a strand from forming and the product from merely advancing through the screw space without the desired turning over, i.e., admixing, reacting, homogenization, treatment, etc. By the use of the scraper fingers or breaker rods, it is widely assured that, depending on the material properties, such as viscosity, hardness, flowability, etc., and also on further process parameters, the deficiencies indicated above are substantially eliminated, or at least are opposed.
The risk of formation of cakes, plastic or semiplastic lumps, strands, etc. during the passage of the material through the treatment zone defined by extruder, expander, or the like, is always present when the product or the material mixture passes, for instance, through a change in its state of aggregation (melting, condensation, solidification, etc.) or when it is worked in a humid atmosphere or one containing solvents, or when changes of viscosity take place as a consequence of the reaction. This is the case when, for instance, among other things, during the processing of foodstuffs, such as noodle or meat products, there occur rheological changes of material, or when feed, or oily or fatty products are extruded at temperatures which are in the range of the melting or saturation of the material so that an agglomeration or caking of the products or the material mixture can hardly be avoided. Only as an example, the so-called thermic conditioning of oilseeds in preparation for solvent extraction is particularly salient. In this treatment in continuous operation, easily plastifiable natural products, such as soybeans and others are quickly compressed and compacted in an hydrated atmosphere and therefore transported then only as a swelling without the desired effects of temperature and humidity taking place to the best. Similar observations were made in the processing of feed mixtures, of starch-containing material or of fertilizer batches, where, particularly with protein-and starch-containing products and when working in a humid atmosphere, additional problems were created due to smudging of the material.
In order to assure the constant changing of the surface of the material during the transport of material through the treatment zone, for example, through the screw volume of an extruder, expander, or the like, which constant changing is required for an optimum turning over of the material and, at the same time, in order to oppose the formation of smudgings, cakes, strands, etc., it has been proposed, as already mentioned above, to insert into the screw volume or into the treatment zone, scraper fingers or breaker rods. These are rigidly attached on the inner wall of the jacket of the apparatus (expander, etc.) and radially oriented toward the screw shaft. Rod-like solid bodies (fingers) which have a circular area of cross-section and may have central bores are involved (see German DE 23 35 333385 or U.S. Pat. No. 3,255,220). The rigid location or attachment of such scraper fingers proved disadvantageous, since it did not permit a modification of the transport path of the material to be treated while the system was in operation or even during the interruption of operation. An unfavorable configuration or habit permitted only a laminar flow of the products around the rods or pins, and the great number of the rods or pins required an extremely high driving power from the screw motor, all the more since they were rigidly mounted. A constantly repeating mixing effect, constant renewal of the product surface, mechanical lifting of the material, crushing of the material or formations of crumbs, and prevention of the formation of merely transported lumps or strands, particularly when working in humid atmosphere or in the temperature range of phase transitions, was only restrictedly possible with the known apparatus.